Ceramic granules with high uv opacity and high solar reflectance

ABSTRACT

The invention relates to ceramic granules with a high UV opacity and high solar reflectance, which is produced by forming a calcined clay mineral powder into green body and re-calcining, featured with a water absorption of 15-35%; ≥97% crystalline content and 90-100% UV opacity. The invention further relates to a method for preparing ceramic granules with a high UV opacity and high solar reflectance and the use thereof for reflectance-improving application on building surface for the purpose of energy conservation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/124,058, filed Sep. 6, 2018, entitled “Ceramic Granules With High UVOpacity And High Solar Reflectance,” the entirety of which isincorporated by reference.

TECHNICAL FIELD

The invention relates to ceramic granules with high UV opacity and highsolar reflectance as well as a method for producing the same. Theceramic granules are suitable for reflectance-improving applications onbuilding surface for the energy conservation purpose.

BACKGROUND OF THE INVENTION

The literatures are cited in the present description for the purpose ofdescribing the state of the art to which the present invention pertains,and are incorporated herein by reference in their entire disclosures.

In order to reduce energy consumption, building codes issued inCalifornia, USA, require that the solar reflectance of low-slope roofsshould be 70% min. It is a very effective heat-shielding technique toadhere highly solar reflective granules on the surface of asphaltroofing materials. Compared with other reflective materials such asplastics, metals, and organic coatings, highly solar reflective granulesare featured by low costs and high aging resistance. Most ofcommercially available white granules, such as quartz, calcite, calcinedkaolin, synthetic ceramic granules usually have high solar reflectivitywhen measured as bulk granules, but have a rather low solar reflectivityafter being applied on black substrate. Furthermore, white granules tendto discolor due to significant oil absorption, which in turn reduces itssolar reflectivity. In addition, the asphalt substrate to which thegranules are embedded would easily degrade due to the low UV opacity ofthe granules.

White granules used on the roof are required to have high whiteness,which significantly limits the source of white granules available forroofing. There are mainly two kinds of highly solar reflective granulesavailable on the market, in which one is obtained by directly calciningspecial raw mineral ore, and another one is obtained by calcining milledraw minerals powder with the addition of a certain amount offlux/fluxing agent. As to the former one, the raw mineral tends tochange its color during calcination, making it difficult to control thequality of the final product. This further limits the source of rawmaterials.

U.S. Pat. No. 9,714,512B discloses a cool roofing system comprisinghighly reflective calcined kaolin granules with solar reflectance of80-92%. The calcined kaolin granules are applied to a roofing substrateafter being coated with a polymeric organic coating, forming a roofsystem with solar reflectance of at least 70%. The bright white calcinedkaolin granules in this invention are restrained by the locations fromwhich the raw materials are mined, and limit their application on themarket.

U.S. Pat. No. 9,944,562 B discloses highly reflective ceramic granulescomprising core particulates and at least one layer of coating, whereinthe sand particulates comprise calcined ammonium illite obtained bycalcining ammonium illite ore at 700-1200° C., and the preparationmethod of the same. The sand core granules, after being coated with aninorganic coating, are calcined at 800 to 1200° C. to obtain ceramicgranules. The ceramic granules have a particle size of 0.1 to 3.5 mm,with a solar reflectance of at least 80% and a staining index DL* ofless than 6%.

US20150192698 discloses highly reflective ultra-white roofing granuleswith a solar reflectance of at least 80%, which are prepared by using ahomogeneous mixture comprising clay, sintered material and optionallyquartz particles.

The market demands for a new roofing granule with high UV opacity andhigh solar reflectance with mass supply. On the other hand, it isdesirable that the raw materials for the preparation of ceramic granulescan be easily obtained economically. It is also desirable that theceramic granules have superior performance in high porosity, highwhiteness, high reflectivity, and low consumption and the like.

Furthermore, it is desirable to prepare ceramic granules with simpleprocedures. It is also desirable to produce a final roofing product thathas high solar reflectance, long service life, and ease of maintenance.

SUMMARY

It was found by the inventors that for clay-based silica-aluminaminerals, high solar reflective granules with high UV opacity tend toresult in high solar reflectance after applied on a black substrate.

According to one or more embodiments of the present invention, theceramic granules are produced by forming a calcined clay mineral powderinto green body and re-calcining. It was found by the inventors that theceramic granules thus produced have high crystalline content, high UVopacity and appropriate crushing strength. Surprisingly, it has alsobeen found by the inventors that such ceramic granules are capable ofachieving high solar reflectance when being applied on asphalticsubstrate. According to one or more aspects of the present invention,ceramic granules with beneficial properties are obtained by controlling,for example, the particle size of the raw material, the whiteness, andparameters of the forming and calcining process.

In one aspect of the invention, calcined clay is used as raw materialfor the ceramic granules. The raw material is widely available and thequality of the products can be easily controlled. Calcined clay powderis widely used in the ceramic industry, refractory industry, fillerindustry and the like, but it has not been reported that it can be usedto produce highly reflective granules for roofing.

In one aspect of the invention, ceramic granules with a high UV opacityand high solar reflectance are produced by forming a calcined claymineral powder into green body and then re-calcined, with waterabsorption between 15-35%, preferably 20-30%; crystalline content ≥97%,preferably 97%-100%; and UV opacity between 90%-100%, preferably92%-100%, more preferably 96-100%.

According to one embodiment, there is a method provided for preparingthe ceramic granules, comprising the steps of: a) providing a suitablecalcined clay powder as raw material; b) mixing the raw material with acertain proportion of water and forming the raw material into a greenbody; and c) calcining the green body at the temperature of 1100-1400°C.; d) crushing the calcined material to obtain granules; e) optionallysurface treating the granules.

In one aspect of the invention, it introduces the use of the ceramicgranules for reflectance-improving application on building surface forthe purpose of energy conservation.

DESCRIPTION OF DRAWINGS

FIG. 1 shows a flow chart for preparing highly reflective ceramicgranules in accordance with one aspect of the present invention.

FIG. 2 shows an X-ray diffraction spectrum of ceramic granules accordingto an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The preparation of highly reflective ceramic granules in accordance withone aspect of the present invention is illustrated below referring toFIG. 1.

The Calcined clay powders, to which water is added, are mixedhomogeneously and then formed into green bodies. The green bodies arecalcined at high temperature in kiln. The calcined material is crushedand sieved to obtain highly reflective ceramic granules.

FIG. 2 shows an X-ray diffraction spectrum of ceramic granules obtainedaccording to Experiment No. 1 of the present invention. As can be seenfrom the figure, the ceramic granules have a crystalline content of100%.

Definitions

The following definitions are used herein to further define and describethe present disclosure. Unless otherwise defined in specific instance,these definitions apply to the terms as used throughout the presentdisclosure.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by those skilled in the artto which the present invention pertains. In case of conflict, thepresent specification, including the definitions given herein, shallprevail.

Unless otherwise indicated, all percentages, parts, ratios, and the likeamounts used herein are defined by weight.

In the present invention, the UV opacity is used to indicate the opacityof an object to light within the ultraviolet range.

In the present invention, solar reflectance (SR) is used to characterizethe ability of a material to reflect back solar radiation incident onits surface.

In the present invention, D₅₀ representing an average particle size ofthe granules is a median diameter of the 50% cumulative volume in aparticle size distribution curve measured by the laser diffractionscattering method.

The crushing index indicates the ability of the granules to resistcrushing, which may be used to evaluate the corresponding strength ofthe granules indirectly.

The water absorption of mineral materials depends mainly on theirporosity. In the present invention, the water absorption is used toindicate the porosity of the ceramic granules.

According to one embodiment, clay suitable for the invention compriseshalloysite, dickite, kaolin, montmorillonite, allophane, ammoniumillite, pyrophyllite or a mixture of one or more thereof. Calcined clayis commercially available from suppliers including, for example, HebeiChida Manufacture and Trade Co., Ltd.

According to one embodiment, the calcined clay powder is selected tohave a particle size D₅₀ of between 0.01 and 8 μm, preferably between0.1 and 6 μm, more preferably between 0.5 and 5 μm.

The color space is a color system represented by L*, a*, and b*. In thepresent invention, the standard used by the L*a*b* color system is theCIE color model, where L* represents the lightness, with L*=0 indicatingblack and L*=100 indicating white. The a* value represents the red-greencomponent of the color, with green in the negative direction and red inthe positive direction. The b* value represents the yellow-bluecomponent of the color, with blue in the negative direction and yellowin the positive direction. According to one embodiment, the color valuesof the calcined clay powder are selected such that L* is between 80 and100, a* is between −5 and +5, and b* is between 1 and 10. According toone embodiment, the color values of the calcined clay powder are: L* ofbetween 85 and 100, a* of between −3 and +3, and b* of between 1 and 9.According to another aspect of the present invention, the color valuesof the calcined clay powder are: L* of between 88 and 100, a* of between−1 and +1, and b* of between 2 and 8. The powder material thus selectedhas a small content of light absorbing material.

According to one embodiment, the crushing index of the ceramic granulesis between 15% and 35%, preferably between 20% and 30%.

According to one embodiment, the solar reflectance of the ceramicgranules is between 82% and 90%.

According to one embodiment, the ceramic granules have a solarreflectance of from 75% to 85% when being applied to an asphalticsubstrate at a coverage of 90% or more. According to another embodiment,the ceramic granules have a solar reflectance of 80% to 90% when beingapplied to a foam (such as polyurethane) substrate at a coverage of 90%or more.

According to one embodiment, no flux/fluxing agent is needed in thecourse of the re-calcination.

According to one embodiment, the calcined clay powder is formed to greenbody and then calcined to obtain granules having a certain strength andretaining a certain amount of pores.

The amount of water required for the forming step itself is known bythose skilled in the art. The amount of water added may be 0% to 100%,preferably 5% to 60%, more preferably 10% to 50% relative to the weightof the calcined clay powder.

Forming Pressure and Forming Method

The forming/moulding pressure has influence on the strength and porosityof the ceramic granules. High pressure leads to high strength and lowporosity of the granules.

The forming/moulding pressure for the green body to be calcined is inthe range of 0-1000 MPa.

High pressure sets forth a high requirement on the forming/mouldingequipment, rendering a higher equipment investment and a more seriouswear. On the other hand, it is difficult to obtain suitable strength ofthe ceramic granules when the moulding pressure is too low.

Generally, the forming/moulding pressure can be selected between 50 to200 MPa.

The forming/moulding of the powder can be conducted, for example, bycasting, pressure moulding or rolling granulation.

Green Body Calcination

The green body can be calcined with heat sources such as electricity,coal, natural gas, fuel oil, etc. The calcining kiln can be a shuttlekiln, a tunnel kiln, a roller kiln, a rotary kiln and the like. If thecalcination temperature is too low, the strength of the preparedgranules is insufficient. If the calcination temperature is too high,the number of pores is gradually reduced, which impacts the reflectionof the granules to solar radiation. According to one aspect of theinvention, the green body is calcined at a temperature from 1100 to1400° C., preferably from 1150 to 1350° C.

Crushing and Sieving

The calcined material obtained by calcining the green body can becrushed with a jaw crusher, a hammer crusher, a cone crusher, a rollcrusher, an impact crusher, a mill, or a combination thereof. Theceramic granules obtained by crushing can be sieved to adjust theirparticle size distribution. As for the sieving device, a fixed sieve, amovable sieve, a vibrating sieve or a combination thereof can be used.In order to make the ceramic granules suitable for roofing material,they are processed into granules having a particle size of from about0.1 to 3.5 mm, preferably from about 0.3 to 2.3 mm, more preferably fromabout 0.5 to 2 mm

Surface Treatment

According to one embodiment, the ceramic granules can be further surfacetreated to obtain functions such as water repellency, stain resistanceand algae resistance. The surface treatment generally includes surfacetreatment selected from inorganic coating, organic coating, waterrepellent or a combination of more than one above treatment thereof.

According to one embodiment, the inorganic coating is a liquid inorganiccoating selected from at least one of silicate, aluminum phosphate,silica sol, and aluminum sol. The silicate is selected from the groupconsisting of sodium silicate, potassium silicate, aluminum silicate,lithium silicate or a mixture of one or more thereof.

According to one embodiment, the organic coating is selected from thegroup consisting of acrylics and silicone-acrylic coating. The waterrepellent may be selected from the group consisting of silanes,silicones, and fluorine-containing water repellents.

The inorganic coating, the organic coating or the water repellent mayfurther comprise one or more selected from the group consisting ofpigments, algaecides, insecticides, self-cleaning agents, viscositymodifiers, fluxing agents, flame retardants, surface tension modifierand anti-aging agents.

According to one embodiment, the ceramic granules further comprise anadditional coating obtained by secondary coating with an organic coatingand/or a water repellent, wherein the organic coating is a resin coatingor an emulsion coating, and the water repellent is a silicon-containingwater repellent or a fluorine-containing water repellent.

Applications

According to one embodiment, the ceramic granules can be applied to thesurface layer of a roofing material with substrate made of cement,asphalt, polyurethane foam or coated metal, so as to increase the roofreflectance to solar radiation. The ceramic granules have a solarreflectance of 75% to 85% when applied on asphaltic substrate at acoverage of 90% or more. According to another embodiment, the ceramicgranules have a solar reflectance of 80% to 90% when being applied tofoam substrate (such as polyurethane foam) at a coverage of 90% or more.

According to one embodiment, the ceramic granules can also be used instone texture coating for buildings to produce a highly reflectivecoating layer, which has the same effect as white granules.

Examples

The following examples are provided to describe the invention in moredetail. These examples, illustrating the specific embodiments andpreferred technique for implementing the present invention, are intendedto illustrate but no to limit the invention.

General Description of the Testing Methods Whiteness

The color value was measured with a colorimeter (Model SC-100,manufactured by Beijing Kangguang Optical Instrument Co., Ltd.).

Take a certain amount of a sample and put into a tablet machine (anaccessory of the colorimeter, Model SC-100, manufactured by BeijingKangguang Optical Instrument Co., Ltd), to be pressed into a tablet. Thetablet is measured for its whiteness with the colorimeter at the flatterside of the tablet. The values of L*, a* and b* were measured for threetimes and an average value was calculated.

Particle Size D₅₀

The particle size D₅₀ was measured with a laser particle size analyzer(Model BT-9300H, manufactured by Dandong Bettersize Instrument Co.,Ltd.)

Water Absorption

Take 50 g ceramic granules, and place it in a beaker with water, andstirred the mixture with a glass rod for 10 s. A piece of cotton clothwas immersed in water, wringed until no water dripping and then unfoldedon a table. The granules immersed in water were removed from the beakerand laid on the cotton cloth. The granules were wiped back and forthwith the cotton cloth until no water stains on the surface of thegranules can be observed (the granules shall be loose and not sticky).Weigh approximately 5-10 g (m1) of the wiped ceramic granules with ascale accurate to 0.1 mg and place into a beaker. The granules weredried in a 105° C. oven to constant weight. The weight (m2) of theceramic granules after drying was measured. The water absorption iscalculated according to the following equation: Waterabsorption=(m1−m2)/m2*100%.

Crystalline Content

The crystalline content was measured with an X-ray diffractometer (ModelD/MAX 2500, Rigaku Corporation, Japan), and calculated.

Crushing Index

The crushing index was measured on ceramic granules with size between1.7 mm and 1.18 mm according to the Part 6.12.2 of GB/T 14684-2001.

UV Opacity

UV opacity was measured similar to ASTM D1866-79.

Instruments: flood lamp box, standard photographic step tablets (Kodakphotographic step tablets, No. 2, calibrated), filter (UV-lighttransparent and visible-light absorbing glass, model ZWB1, NantongRuisen Optical Element Technology Co., Ltd), camera (Panasonic DMC-GF5),template (a perforated board with 110 holes).

Procedure

The flood lamp box consists of a box and a flood lamp (PHILIPS, Model:RVP350 L 1XHPI-T 400W IC220V50 Hz SP SY) installed in the box. There wasa square opening on the top of the box, and the light emitted from theflood lamp was illuminated upward through the square opening. The filterwas fixed above the square opening with a filter slide, and the templatewas placed above the filter. Turn on the flood lamp for 10 minutes towarm up the apparatus.

Screen the ceramic granules using a Tyler 10 mesh and Tyler 12 meshscreen and take 5 g sample of 10-12 mesh. Place one granule in eachspace of the template with tweezers. Adjust the granule to make sureeach hole is completely covered and there was no light transmit. Then,place the upper template and check for light transmission. If there waslight transmitted, adjusted the granule until there was no lighttransmitting through the hole.

A standard graphical step tablets was carefully cut lengthwise down thecenter to produce two equal tablets. One tablet was laid on the otherone so that the 14th step of the bottom tablets was situated below the1st step of the upper tablets (Note: Don't count the clear area. Thedark steps of both step tablets should on the left side. Secure the twostep tablets with two tapes on both ends). The combined step tablets wasplaced on the 10 holes at the bottom of the lower template. Make surethe 14^(th) step of the bottom tablet and the 1st step of the uppertablet are squarely over the 5^(th) hole from the left. Secure thetablets with tapes. Make sure all the holes are completely covered bythe step tablets and that the tape does not block the holes.

Fix a camera right above the square opening with a camera holder. Turnoff the room lights and make sure it is in completely darkness. Takephotos with the camera.

Open the photos with Photoshop software in a computer. Adjust thecontrast of the photos so that the brightness of the 5th hole from theleft of the step tablets is barely seen, and count the number of brightspots on the photo (the number of holes n). Calculate UV opacityaccording to the following equation:

UV opacity=(number of granules placed−number of brightspots)/100*100%=(100−n)/100*100%.

Solar Reflectance (Ceramic Granules)

The solar reflectance was measured in accordance with the ASTM-C1549standard. The reflectance of the sample was measured with a solarspectrum reflectometer (model SSR-ER, A&D, USA). Set the reflectometerin b891 output mode for measurement. 50 g granules sample was placed ina flat sample tray, and then levelled and smoothed with a ruler. Solarreflectance was measured on three points randomly selected on thesurface.

Solar Reflectance (after being Applied to Asphalt Substrate)

The solar reflectance was measured in accordance with the ASTM-C1549standard. The reflectance of the sample was measured with a solarspectrum reflectometer (model SSR-ER, A&D, USA). Adjust thereflectometer to the b891 output mode for measurement. A sufficientamount of granules were evenly spread on the low-melting sticky asphaltboard, flattened, and the loose granules on the surface were removed.Solar reflectance was measured on three points randomly selected on thesurface of the asphalt substrate.

Experiment Series 1

Calcined clay powders, uncalcined powder and raw ore from China HebeiChida Manufacture and Trade Co., Ltd. were employed, the properties ofwhich are summarized in Table 1.

TABLE 1 Properties of raw materials employed Calcined clay Powder powderD₅₀ value, whiteness whiteness whiteness number Mineral μm L* a* b* 1Calcined 0.5 μm 93 0 3 ammonium illite powder 2 Calcined 4.0 μm 93 0 3ammonium illite powder 3 Calcined 10 μm 93 0 3 ammonium illite powder 4Calcined 4.0 μm 93 1 3 kaolin powder   1a ammonium 0.5 μm 50 0.7 3.4illite powder (uncalcined)   2a ammonium 4.0 μm 50 0.7 3.4 illite powder(uncalcined)   3a ammonium 10 μm 50 0.7 3.4 illite powder (uncalcined) 1b ammonium / 45 0.8 3.6 illite ore (uncalcined)

The preparation of Ceramic granules from calcined clay powder was asfollows.

Place 10 kg calcined clay powders listed in the table 1 and 2 kg waterinto a mixer [Gongyi City Zhanjie Wandu Machinery Factory, Model 000] tomix evenly. The mixed powders were pressed into 240*115*53 mm greenbodies with a 100 tons press [Beijing Zhongcai Jianke Industry & TradeCo., Ltd., model ZCY-200]. The green bodies were then calcined in a hightemperature furnace at 1250° C. [Luoyang Hengli Kiln Co., Ltd., modelHLX17C] for 10 h. After cooling, the calcined materials were crushedwith a crusher [Hebi city Three Long Electronic Technology Co., Ltd.,Model CP-180×150] to granules with the size of about 0.5-2 mm. Thegranules were tested with respect to their UV opacity, SR (ceramicgranules), and SR (after applied to asphalt substrate).

The preparation of Ceramic granules from uncalcined clay powder is asfollow.

The preparation of ceramic granules from uncalcined clay powder was thesame as with calcined clay powder, except the calcining time of theformer is about 30 hr. The purpose of extending the calcination time isto turn the uncalcined clay powder into white.

Ceramic granules were prepared from raw mineral ore according to thefollowing procedure:

About 10 kg of the ore were weighed and put into a high temperaturefurnace[Luoyang Hengli Kiln Co., Ltd., Model HLX17C]. The ore wereheated therein at 1250° C. for 30 h. After cooling, the ore was crushedwith a crusher [Hebi City Three Long Electronic Technology Co., Ltd.,Model CP-180×150] to about 0.5-2 mm granules. The granules were testedwith respect to their UV opacity, SR (granules as produced), and SR(after applied to asphalt substrate).

TABLE 2 Properties of the ceramic granules Granules on the Powder/asphalt Experiment ore UV Granules, substrate, Crystalline No. usedopacity % SR % SR % content % 1 1 100 90 83 100 2 2 99 89 81 100 3 3 8588 74 100 4 4 99 88 81 100 5   1a 100 83 74 100 6   2a 99 80 73 99 7  3a 82 80 70 99 8  1b 78 82 67 99

As can be seen from the above table, even with different UV opacity, thegranules have similar SR values. However, when applied to asphaltsubstrate, the granules of higher UV opacity tend to result in highersolar reflectance.

Experiment Series 2

Procedure for preparing the ceramic granules:

Place 10 kg of calcined clay powder listed as No. 1 in table 1 and 2 kgwater into a mixer [Gongyi City Zhanjie Wandu Machinery Factory, Model000] and mix evenly. The mixed powders were pressed into 240*115*53 mmgreen bodies with a 100 tons press [Beijing Zhongcai Jianke Industry &Trade Co., Ltd., Model ZCY-200]. The green bodies were then heated in ahigh temperature furnace [Luoyang Hengli Kiln Co., Ltd., Model HLX17C]for 10 h at temperature of 1050° C., 1150° C., 1280° C. and 1450° C.,respectively. After cooling, the bodies were crushed with a crusher[Hebi city Three Long Electronic Technology Co., Ltd., Model CP-180×150]to granules with the size of about 0.5-2 mm. The granules were testedfor UV opacity, SR (ceramic granules), SR (granules on asphaltsubstrate) and the crushing index to evaluate the influence of thecalcination temperature.

TABLE 3 Properties of the ceramic granules Granules Calcination Water UVGranules on the asphalt Crushing Crystalline temperature absorption %opacity % SR % substrate, SR % index % content % 1050 50 100 90 82 40 951150 30 100 90 82 30 98 1280 25 99 88 80 20 100 1450 10 80 88 70 15 100

As can be seen from the above table, a low calcination temperature tendsto result in low granule strength, while a high calcination temperaturetends to result in low UV opacity.

1. Ceramic granules having a high UV opacity and high solar reflectance,produced by forming a calcined clay mineral powder and re-calcining,wherein the ceramic granules are characterized by: 15-35% waterabsorption; ≥97% crystalline content; 90-100% UV opacity; and a solarreflectance of between 82% and 90%.
 2. The ceramic granules according toclaim 1, which have a water absorption of between 20% and 30%.
 3. Theceramic granules according to claim 1, which have a crystalline contentof between 97% and 100%.
 4. The ceramic granules according to claim 1,which have a crushing index of from 15% to 35%.
 5. The ceramic granulesaccording to claim 1, which have a UV opacity of between 92% and 100%.6. The ceramic granules according to claim 1, wherein the clay comprisesdickite, kaolin, montmorillonite, pyrophyllite, halloysite, allophane,ammonium illite or a mixture of one or more thereof.
 7. The ceramicgranules according to claim 1, wherein the calcined clay powder has aparticle size D₅₀ of between 0.01 μm and 8 μm.
 8. The ceramic granulesaccording to claim 1, wherein the calcined clay powder has an L* between85 and 100, a* between −3 and +3 and b* between 1 and
 9. 9. The ceramicgranules according to claim 1, wherein the forming of the calcined claymineral powder is conducted by casting, pressure moulding or rollinggranulation.
 10. The ceramic granules according to claim 1, wherein theceramic granules have a particle size of 0.1 to 3.5 mm.
 11. The ceramicgranules according to claim 1, wherein the ceramic granules are surfacetreated, and the surface treatment is selected from inorganic coating,organic coating, water repellent or a combination of more than one abovetreatment thereof.
 12. A system, comprising: a substrate formed of anasphaltic substrate, a polyurethane foam substrate, cement substrate ora coated metal substrate; and the ceramic granules of claim 1 applied tothe top surface of the substrate.
 13. Ceramic granules having a high UVopacity and high solar reflectance, produced by forming a calcined claymineral powder and re-calcining, wherein the ceramic granules arecharacterized by: 15-35% water absorption; ≥97% crystalline content;90-100% UV opacity; and the resultant ceramic granules have a solarreflectance of from 75% to 85% when applied to asphaltic substrate at acoverage of 90% or more.
 14. The ceramic granules according to claim 13,wherein the ceramic granules have a particle size of 0.1 to 3.5 mm. 15.The ceramic granules according to claim 13, wherein the ceramic granulesare surface treated, and the surface treatment is selected frominorganic coating, organic coating, water repellent or a combination ofmore than one above treatment thereof.
 16. Ceramic granules having ahigh UV opacity and high solar reflectance, produced by forming acalcined clay mineral powder and re-calcining, wherein the ceramicgranules are characterized by: 15-35% water absorption; ≥97% crystallinecontent; 90-100% UV opacity; and the resultant ceramic granules have asolar reflectance of between 80% and 90% when applied to the surface ofa polyurethane foam substrate at a coverage of 90% or more.
 17. Theceramic granules according to claim 16, wherein the ceramic granuleshave a particle size of 0.1 to 3.5 mm.
 18. The ceramic granulesaccording to claim 16, wherein the ceramic granules are surface treated,and the surface treatment is selected from inorganic coating, organiccoating, water repellent or a combination of more than one abovetreatment thereof.